(a) Field of the Invention
This invention relates to a dry type toner for developing an electrostatic latent image, particularly, a toner containing the specific compound as a charge controlling agent (polarity controlling agent).
This invention further relates to a toner for developing an electrostatic latent image, which comprises a combination of the specific binder resin and said specific charge controlling agent (polarity controlling agent).
(b) Description of the Prior Art
There are two types of systems for developing electrostatic latent images formed on an electrophotographic photosensitive material, electrostatic recording material and the like, one of which uses a wet type liquid developer (wet type developing method), and the other of which uses a dry type developer containing, for example, one component type toner having a coloring agent dispersed in a binder resin or two component type toner comprising a mixture of said one component type toner with a solid carrier (dry type developing method). These systems respectively have merits and demerits. Recently, the dry type developing method, particularly a two component type developer is generally used.
It is usual for the above mentioned toner (developing powder) to add an appropriate amount of a charge controlling agent (polarity controlling agent) to impart desired electrification properties since a toner prepared simply by dispersing a coloring agent such as dye, pigment and the like in a binder resin without adding any charge controlling agent does not have satisfactory electrification properties.
Examples of the conventionally known charge controlling agents include (i) an agent for imparting a positive charge to a toner such as nigrosine type dye and (ii) an agent for imparting a negative charge to a toner such as metal-containing dyes, for example, chromium-containing monoazo complex, metal complex of salicylic acid, chromium-containing salicylic acid compound complex, chlorine-containing organic dye (Copper Phthalocyanine Green, chlorine-containing monoazo dye), and the like. However, most of these conventional charge controlling agents have disadvantages that they are colored materials, that they have poor compatibility or wetting property with a binder resin, or that their charge controlling properties do not remain long because of subliming property. Thus, most of them are unsuitable as a charge controlling agent for a toner of electrophotography, particularly a color toner for use in a color copier. A toner containing these conventional charge controlling agents has favourable developing properties at the initial stage, but its life is short. It sometimes reverses electrification, thus the electrification properties (Q/M) being quite unstable. Moreover, its environmental stability is poor (stability to the changes of temperature and moisture is poor). In addition to these disadvantages, the transferring properties of the toner are poor when making multi-color copies such as three color copies or four color copies.
The above mentioned conventional coloring agents and charge controlling agents are disclosed in Japanese Patent Publication Nos. 48-25941, 48-26784, 49-20225, 46-43440, 48-30899, 49-46423 and 49-26909, and Japanese Patent Laid Open Nos. 50-140137, 50-142037, 50-142038, 49-51949, 49-134303 and 60-46566.
It is known to use a chlorinated paraffin, unsaturated polyester and the like as a binder resin for making a toner negatively electrified, or to use the specific polyester resin having a kind of cross-linking structure (reaction product of non-linear low melting aromatic resin with chelated salicylic acid) (see Japanese Patent Laid Open No. 59-29259), but these resins do not have a molecular weight desired for a binder resin, thus not having appropriate heat-properties (appropriate melting properties by heat roll during fixing) demanded for a toner. Therefore, these resins provide various problems as copy delivery miss caused by the winding of a copy about a heat roll, and "off-set" phenomenon that a developed image becomes unclear because a toner on a copy paper is tranferred to the surface of a roller.
It is also known to use metal complex of salicylic acid as a charge controlling agent (see Japanese Patent Publication No. 55-42752), but this compound is a colored chelated compound. Since this compound is not colorless but colored, it is not suitable for a color toner.